1. Field of the Invention
The present invention relates to a laminated film having a high heat-sealability and comprising a substrate of poly(4-methyl-1-pentene).
2. Description of the Related Art
The good transparency, heat resistance, chemical resistance and the like, of poly(4-methyl-1-pentene) have led to the application thereof to laboratory ware such as beakers or graduated cylinders, syringes, cells for optical measurement, trays for microwave ovens, and a baking carton comprising a paper coated therewith, etc. But although poly(4-methyl-1-pentene) has a high melting point and a good heat resistance, it has a disadvantage in that it has a poor heat-sealability. The most generally used method for improving this heat-sealability is by lamination of the poly(4-methyl-1-pentene) with a resin such as polyethylene or polypropylene having a good heat-sealability and a lower melting point. But, poly(4-methyl-1-pentene) and polyethylene or polypropylene do not adhere to each other, although they are both a polyolefin, and thus a product prepared by laminating these elements cannot be practically employed.
Further, if the poly(4-methyl-1-pentene) film is laminated with a polyethylene film by applying an adhesive based on a urethane as an anchor coating agent, the heat-sealability is not greatly improved because the poly(4-methyl-1-pentene) film has a poor surface-wettability, and thus the resulting laminated film has a low adhesive strength.
The assignee of the present application has already filed Japanese Patent Application No. 59-1387 Unexamined Publication No. 60-145844) which discloses that a laminated film having an improved adhesive strength and a high heat-sealability can be obtained by employing a particular random copolymer of propylene and .alpha.-olefin as an adhesive layer for the lamination of poly(4-methyl-1-pentene) film and a polyethylene or polypropylene film.